Nowadays, electronic ballasts are widely used because of advantages such as high efficiency, light weight, and absence of flicker and audible noise over the electromagnetic ballasts. Among the various electronic ballasts for driving light emitting elements (e.g., fluorescent lamps), the self-oscillating electronic ballast is simple and low cost.
However, the self-oscillating electronic ballast has problems as follows. In a self-oscillating circuit, the working frequency of the self-oscillating resonant circuit is determined by load and the nature of its circuit structure, thus it is very difficult to control the output of the self-oscillating electronic ballast. Consequently, the working current or power of light emitting elements is hard to control. In addition, the working frequency of the conventional self-oscillating electronic ballasts and the power of light emitting elements depend on characteristics of driving transformers in the self-oscillating electronic ballasts. For a batch of self-oscillating electronic ballasts with the same circuit design, manufacturing differences of the driving transformers may lead to that light emitting elements in the same batch have different working current.
Therefore, there is a demand for electronic ballast whose working frequency can be controlled so as to make the working current or power of light emitting elements adjustable.